Scanning antenna having a spherical main reflector with moveable subreflector

ABSTRACT

An antenna having a large spherical reflector and a small reflector, wherein the main lobe may be oriented with respect to the large spherical reflector by virtue of the displacement of the small reflector, these displacements being rotations around the center of curvature of the large reflector, and the waves irradiating the small reflector being spherical around the same center, the beam formed by these waves shifting with the displacement of the small reflector.

O United States Patent [151 3,641,577 Tocquec 1 Feb. 8, 1972 [54] SCANNING ANTENNA HAVING A 3,534,373 10/1970 Gustincic etal ..343/771 SP ER] AL M [N REFLE [TH 2,609,505 9/1952 Pippard ..343/76l g g w 2,677,056 4/1954 Cochrane et al ..343/754 2,975,419 3/1961 Brown ..343/754 1 72 inventor; Yves Tocquec, Marcoussi France 2,986,734 5/1961 Jones et al. .....343/754 3,195,137 7/1965 Jakes ..343/756 Asslgneer v g Generale dElec-tncite, Pans. 3,241,147 3/1966 Morgan ..343/78l France 3,332,083 7/1967 Broussaud ..343/761 [22] Filed: Man 12, 69 3,383,692 5/1968 Laibson et al. ..343/781 [21] App1.No.: 806,458 Primary ExaminerEli Lieberman AttorneyCra.ig, Antonelli & Hill [30] Foreign Application Priority Data [57] ABSTRACT Mar. 12, 1968 France ..l434l8 An antenna having a large Spherical reflector and a Small reflector, wherein the main lobe may be oriented with respect U.S. l to the large spherical reflector virtue of the displacement of 343/786, 343/839 the small reflector, these displacements being rotations [51] Int. Cl. ..H0lq 19/14 around the center of curvature of the large reflector, and the [58] Field of Search ..343/753, 754, 761, 781, 840, waves irradiating the small reflector being spherical around 343/786, 839 the same center, the beam formed by these waves shifting with the displacement of the small reflector. 56 R f ted 1 e mm m a A 13 Claims, 7 Drawing Figures UNITED STATES PATENTS w 2,976,533 3/1961 Salisbury "343/761 PATENTEDFEB 8 m2 3.641.577

sum 3 or FIG.4

PATt'NfEUFE B 8 I972 SHEET '8 OF 4 FIG.6

SCANNING ANTENNA HAVING A SPHERICAL MAIN REFLECTOR WITH MOVEABLE SUBREFLECTOR The present invention relates to radio antennas with an orientable or adjustable major lobe and is concerned more particularly with very large-size antennas comprising a large reflector whose configuration is essentially that of a spherical cap.

Such a reflector may have a diameter in the order of about 100 meters, for example. It must be nondeformable, by the action of the wind particularly, and therefore must be relatively heavy; and, it is expensive to build such antennas in a manner such that they can be adapted to be oriented or adjusted. Antennas ofxthis type are designed, however, especially for establishing communications with artificial satellites which are placed in orbit around the earth for purposes of telecommunication. Now, since such satellites canscarcely be rendered completely. immoyable with respect to the earth, the emission lobe'of maximuni fpower, or the reception lobe of maximum sensitivity, ofthe antenna musttherefore be orientable or adjustable, and the angular variation possible must be in the order of at least several degrees of variation.

The possibility of orientation or adjustment of the lobe with respect to the .axis of the antenna with a slight angular variation in the order of several degrees is desirable even in the case of an orientable or adjustable antenna. A precise positioning a very large-size antenna is difficult andcostly. Hence, 7

after having set or fixed theantenna in a suitable approximate direction, it may be desirable to displace, or adjust the direction of the major lobe by action upon asmall element of the antenna, for example, the source of emission or a small reflector. A

For this purpose it is known to fix the. large reflector with respect to the ground and, in the case where the antenna is utilized for emission, to irradiate it by means of a small reflector,disposed in proximity to the focal point thereof. When the source of emission can be considered as punctiform, which is generally the case, the shape of the small reflector is chosen in such a manner as to couple the point of emission with the focal point of the large reflector in such a way that the waves received by this large reflector seem -to diverge from this point, so that as a result the beam emitted by the large reflector is composedof essentially, parallel waves. In the case of an orientable large reflector it is possible toobtain from such a punctiform source a rigorous parallelism for the emitted beam (if the diffraction phenomena are disregarded).

lt suffices therefore to provide the large reflector with the shape of a paraboloid of revolution and the-small reflector with the shape of an ellipsoid or hyperboloid of revolution, one of the two focuses of the small reflector being positioned on the emission source and the other one of thesetwo focuses coinciding with the focus of the large reflector. This favorable situation cannot be maintained when the direction of the emitted beam must be made to vary with respect to the axis of the large reflector. The latter must then be considered as no longer consisting of one focus but a focal surface each of the points of which plays the role of focus for a specific orientation of the'emitted beam. The small reflector is then utilized for focusing the radiations on the suitable point of the focal surface. The position of the small reflector must therefore vary as a function of the point in question. Under these conditions, the stigmatism of the optical system being constituted in this manner, that is to say, in practice, the parallelism of the emitted beam, can only be approximate. For the purpose of improving it, it is known to provide the large reflector with a shape which departs from that of a paraboloid and approaches that of a spherical cap, and to provide the small reflector with a shape which is more or less complex and designed to compensate as much as possible for the aberrations that are introduced by the large reflector.

It is quite evident that, in order to ensure in the best possible manner this compensation, that is to say, to obtain a parallel emerging beam, it would be of interest to adjust not only the position and orientation of the small reflector as a function of the desired orientation for the emerging beam, but to adjust also the shape thereof. Such an adaptation of the shape of the small reflector obviously requires complex and expensive control mechanisms-On the other hand, even if the shape of the small reflector is invariable, the adjustment of its position and of its orientation,-in the interest of minimizing the aberrations while still ensuring the desired direction of the emerging beam, necessitates complicated calculations and in practice the use of a computer. The drawbacks described hereinabove are present in precisely the same form regardless of whether the antenna isused for transmission or for reception,'and, the problem in bothinstances being that of effecting correspondence between a large parallel beam of plane electromagnetic waves and a beam of spherical waves centered on either an emitting or a receiving member, which will hereinafter be referred to as a source, this source consisting in practice oftentimes of a hom, performing the functions of both the emitter or the receiver properly speaking.

The aforementioned difficulties are encountered on the other hand regardless of the type of antenna mounting which is used. For example, certain antennas of the type in question are known under the name of Casse'grainian" antennas when the small reflector is placed between the large reflector and the focal point of the latter, and. as Gregorian" antennas.

posing variable-phase displacements on the waves which pass therethrough.

The present invention renders it possible to obviate the drawbacks and difficulties outlined above.

. The antenna having an orientable or adjustable lobe as proposed by the present invention comprises a large stationary reflector having theshape of a spherical cap and an intermediate optical system through which pass the radioelectric waves between this large reflector and a source. This source consists of an emitter of radioelectric waves, if the antenna is used for emission; it consists instead of .a receiver, if theantenna is used for reception. The intermediate antenna system is movable with respect to the large reflector in such amanner that the orientation or adjustment of the lobe is determined b the position of this antenna system. 1

' The antenna according to the present invention is characterized by the fact. that'the intermediate antenna system is movable by rotation around the center of curvature of the large reflector and that this intermediate antenna system is adapted to couple .the center of curvature with the focal point I of this large reflector, means being additionally provided to ensure that the waves which are emitted by the source or to which this source is sensitive have spherical wave surfaces centered on this center of curvature.

In order to explain the significance of the present invention, it is expedient to consider the geometrical configuration, in the case of emission for example, of the small and the large reflectors and of the waves arriving on these reflectors and being reflected by them. If one disregards the limitations introduced by the edges of the beam irradiating the small reflector and by those of the small reflector and of the large reflector, it is easy to see that, in accordance with the present invention, the geometrical pattern is maintained identically when the small reflector is displaced.

It thus follows that, if the shape of the small reflector has been determined for purposes of minimizing the aberrations for a certain direction of the emitted beam, these aberrations will be minimized no matter what direction is chosen for the emitted beam and no matter what is the corresponding position of the small reflector.

These and other features of the present invention will become more apparent from the following detailed description thereof, when taken in conjunction with the accompanying drawings, which illustrate several embodiments of the present invention, and wherein FIG. 1 is a schematic diagram of an antenna arrangement in accordance with the present invention;

FIG. 2 is a partially schematic structural view of an antenna according to FIG. 1;

FIG. 3 is a detail perspective view of a small reflector and adjustable support therefor;

FIGS. 4 and 5 are schematic diagrams of alternative embodiments of the invention, respectively; and

FIGS. 6 and 7 are schematic diagrams illustrating beam patterns in connection with an antenna in accordance with the present invention.

FIGS. 1 to 3 illustrate a first embodiment of the present invention including, in a manner known per se, a large reflector 1 having the shape of a spherical cap whose center of curvature is positioned at point 0. A horn 2 is connected to this reflector l by means of a surface 3, the horn being directed at the surface 3 and opening out at the approximate center of the reflector 1. According to the invention, this surface 3 is geometrically part of an ellipsoid, one of the focuses of which coincides with the center of the large reflector l and whose other focus F is positioned on the geometrical axis z, z of the horn 2 preferably at the vertex of the latter.

A small reflector 4 is preferably disposed essentially halfway between the surface 3 and the point 0, the antenna being then of the Gregorian type, in the case of FIG. 1.

FIG. 2 illustrates more completely the'structural arrangement of the antenna according to FIG. 1. Shown in this figure is the small reflector 4 supported by a swivel or ball-andsocket joint 5 connected by means of arms 6, 6' to a caisson 7 which in turn is carried or supported by leg supports 8, 8' secured to the principal reflector l.

The front of this caisson 7, with respect to the reflectors, is inclined about 45 on the axis of the reflector l, and the apparent surface of this inclined member is above that of the small reflector 4 so that the parasitic portion of the beam emitted by the elliptical reflector 3 towards the reflector 4 that is to say, the portion passing to the side of the latter-is returned or reflected in a direction which is as little disturbing as possible, at 90 from the direction of the principal lobe.

In an antenna which is constituted in this manner and used for transmission a source of waves 2' is connected to the vertex of the horn 2 and the elliptical wall '3 of the horn then radiates a wave which converges toward the center of curvature 0 of the large reflector. The phase surfaces" of this wave consequently are spheres which have as their center this center of curvature 0. Under these conditions, a rotation of the small reflector 4 by a certain angle around this center causes a rotation of the wave emitted by the antenna which has the same angular value and the same direction.

FIG. 3 shows a device which may be used for supporting the auxiliary reflector while permitting displacement thereof in two orthogonal directions. In this device, two plates 12 and 13 cooperate by means of cylindrical surfaces in such a manner as to allow for a displacement of the reflector 4 in the direction X, while the plate 13 and the base 14 similarly cooperate by means of cylindrical surfaces oriented in such a manner as to allow for a displacement in the direction Y perpendicular to X. By means of the coordination of these two movements, the reflector 4 may thus be displaced along a spherical surface whose center coincides with the center of curvature 0 of the large reflector.

FIGS. 4 and 5 illustrate schematically other embodiments of antennas as proposed by the present invention.

In the embodiment of FIG. 4, the horn 2 is disposed along the axis of the large reflector l on the convex side of the latter, and an electromagnetic lens 15 is positioned at the opening of this horn in the reflector so as to obtain a wave which is centered at 0, the center of curvature of the large reflector 1.

In the embodiment of FIG. 5, a horn 16 or other conventional primary wave source, for example, a Yagi antenna, is disposed at the center of the large reflector l and oriented toward the latter, and either a dielectric or a metallic lens 17 is located approximately halfway between this horn l6 and the principal reflector 1. In this case, the waves are likewise centered at 0, the center of curvature of the large reflector, but they are divergent at the emission.

The device according to FIG. 3 may be used for the displacement of the lens 17, the latter being supported by an arm so as to prevent the plate from being placed in the field thereof. Any displacement of the lens around the center of curvature 0 of the large reflector produces a rotation of the wave beam emitted by the antenna having the same angular value and the same direction. It is then of advantage to cause the horn 16 to pivot around the point 0 so that the beam which it emits remains centered on the lens 17.

In FIG. I, the edges of the beam of waves have not been defined. FIGS. 6 and 7, being analogous to FIG. 1, represent the position of these edges when the beam emitted by the antenna must be parallel to the axis of the large reflector, and when this beam mustbe removed or distant from this axis, respectively.

In these figures, reference numeral 20 represents an emission horn pivoting around the point F. This horn radiates over a variable portion of the elliptical mirror 3, according to the orientation thereof. This orientation is controlled by mechanical adjusting means 24 for regulating the position of the small reflector 4 in such a manner that the beam being reflected by the elliptical mirror 3 toward the small reflector 4 is centered on the latter at all times. On the other hand, the aperture of the beam emitted by the horn 20 is such that the width of the beam irradiating the small reflector 4 is essentially equal to the width of this reflector. The latter focuses the beam in a point on the focal surface 22 of the large reflector 1. This focal surface is a spherical portion having its center at the center 0 and having half the radius of that of the sphere of which the large reflector l constitutes a cap portion.

The beam then diverges from this point on the focal surface and reaches the large reflector l where it gives rise to a parallel emission of the beam. The direction of this emission is parallel to the straight line joining the center of curvature 0 with the center of the small reflector 4.

This provision allows for using in the best possible manner, on the one hand, the power emitted by the horn 20 and, on the other hand, the surface of the small reflector 4. As to the surface of the large reflector 1, it is always utilized in part only. But it would obviously be possible to reduce the size of this surface in order that it will be completely utilized. In this case, a portion of the power emitted by the horn 20 would be lost when the direction of emission were removed or distant from the axis of the large reflector l.

I have shown and described several embodiments in accordance with the present invention. It is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art and I, therefore, do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art. 1

I claim: comprising 1. An antenna having an orientable major lobe comprising a first relatively large reflector having the shape of a spherical cap,

a transducer for emitting or receiving electromagnetic waves, and

an intermediate optical system for transmitting said waves between said large reflector and said transducer,

said intermediate optical system including first means movable at least in part and displaced with respect to the center of curvature of said large reflect or by rotation around the center of curvature thereof for coupling said center of curvature to a focal point of said large reflector and second means for ensuring that the waves associated with said transducer have spherical wave surfaces centered on said center of curvature of said large reflector, wherein said first means includes a second relatively small reflector positioned in proximity to the focus of said large reflector, said transducer being positioned on the opposite side of said large reflector from said small reflector with said waves being transmitted to and from said small reflector through an opening in said large reflector.

2. An antenna as defined in claim 1 wherein said second means includes a third elliptical reflector connected to said large reflector to provide a surface contiguous thereto and having the shape of a portion of an elongated ellipsoid of revolution, the first focus of said ellipsoid being located at the center of curvature of said large reflector and the second focus thereof being located at the position of said transducer.

3. An antenna as defined in claim 2 wherein said second means further includes a horn cooperating with said third elliptical reflector to couple said waves between said transducer and said opening in said large reflector..

4. An antenna as defined in claim 3 wherein the path from said transducer to said elliptical reflector through said horn is transverse to the axis of said large reflector.

5. An antenna as defined in claim 1 wherein said second means includes an electromagnetic lens positioned in said opening in said large reflector and a horn coupling said transducer to said opening along a line coextensive with the axis of said large reflector.

6. An antenna as defined in claim 1 wherein said second means includes a horn coupling said transducer to said opening in said large reflector.

7. An antenna as defined in claim 2 wherein said small reflector is supported on adjustable mounting means for providing movement of said small reflector over a spherical surface having a center coincident with the center of curvature of said large reflector.

8. An antenna as defined in claim 7 wherein said transducer is directional and mounted for adjustment as to the direction of emission and reception of waves about said second focus.

9. An antenna as defined in claim 8 wherein said intermediate optical system further includes adjusting means for coordinately adjusting the relative positions of said transducer and said small reflector so that waves associated with said transducer are reflected at all times only over the entire useful surface of said small reflector.

10. An antenna having an orientable major lobe comprising:

a first relatively large fixed reflector having the shape of a spherical cap;

a transducer for emitting or receiving electromagnetic spherical waves;

a second relatively small reflector cooperating with said large reflector;

said small reflector being positioned in proximity to the focal surface of said large reflector and shaped for correcting spherical aberrations of said large reflector in such a way that plane waves reflected by the same small reflector after having been reflected by said large reflector are so converted into spherical waves;

said small reflector including means movable at least in part with respect to said large reflector for providing movement of said small reflector over a spherical surface centered at the center of curvature of said large reflector in such a way that this movement is a rotation around said center of curvature;

wherein said small reflector is shaped for said plane waves to be converted into spherical waves centered at said center of curvature;

said transducer being positioned on the convex side of said large reflector for emitting or receiving spherical waves centered at a fixed point; and

fixed transmitting means being positioned in view of an opening through said large reflector for transmitting said waves between said small reflector and transducer through said opening in such a way that spherical waves centered at said center of curvature are converted into spherical waves centered at said fixed point.

11. An emissive antenna as defined in claim 10, in which said transducer is directional and is mounted for adjustment with respect to the direction of emission and reception of waves about said fixed point, and wherein said movable means includes means for coordinately adjusting the relative positions of said transducer and said small reflector so that waves emitted by said transducer are reflected by said transmittin means at all times only over the entire useful surface of sai small reflector.

12. An emissive antenna as defined in claim 11, wherein said transmitting means between said transducer and said small reflector includes a third elliptical reflector connected to said large reflector on the convex side thereof to provide a surface contiguous thereto, and having the shape of a portion of an elongated ellipsoid a first focus thereof being located at the center of curvature of said large reflector and the second focus thereof being located at said fixed point. 

1. An antenna having an orientable major lobe comprising a first relatively large reflector having the shape of a spherical cap, a transducer for emitting or receiving electromagnetic waves, and an intermediate optical system for transmitting said waves between said large reflector and said transducer, said intermediate optical system including first means movable at least in part and displaced with respect to the center of curvature of said large reflector by rotation around the center of curvature thereof for coupling said center of curvature to a focal point of said large reflector and second means for ensuring that the waves associated with said transducer have spherical wave surfaces centered on said center of curvature of said large reflector, wherein said first means includes a second relatively small reflector positioned in proximity to the focus of said large reflector, said transducer being positioned on the opposite side of said large reflector from said small reflector with said waves being transmitted to and from said small reflector through an opening in said large reflector.
 2. An antenna as defined in claim 1 wherein said second means includes a third elliptical reflector connected to said large reflector to provide a surface contiguous thereto and having the shape of a portion of an elongated ellipsoid of revolution, the first focus of said ellipsoid being located at the center of curvature of said large reflector and the second focus thereof being located at the position of said transducer.
 3. An antenna as defined in claim 2 wherein said second means further includes a horn cooperating with said third elliptical reflector to couple said waves between said transducer and said opening in said large reflector.
 4. An antenna as defined in claim 3 wherein the path from said transducer to said elliptical reflector through said horn is transverse to the axis of said large reflector.
 5. An antenna as defined in claim 1 wherein said second means includes an electromagnetic lens positioned in said opening in said large reflector and a horn coupling said transducer to said opening along a line coextensive with the axis of said large reflector.
 6. An antenna as defined in claim 1 wherein said second means includes a horn coupling said transducer to said opening in said large reflector.
 7. An antenna as defined in claim 2 wherein said small reflector is supported on adjustable mounting means for providing movement of said small reflector over a spherical surface having a center coincident with the center of curvature of said large reflector.
 8. An antenna as defined in claim 7 wherein said transducer is directional and mounted for adjustment as to the direction of emission and recEption of waves about said second focus.
 9. An antenna as defined in claim 8 wherein said intermediate optical system further includes adjusting means for coordinately adjusting the relative positions of said transducer and said small reflector so that waves associated with said transducer are reflected at all times only over the entire useful surface of said small reflector.
 10. An antenna having an orientable major lobe comprising: a first relatively large fixed reflector having the shape of a spherical cap; a transducer for emitting or receiving electromagnetic spherical waves; a second relatively small reflector cooperating with said large reflector; said small reflector being positioned in proximity to the focal surface of said large reflector and shaped for correcting spherical aberrations of said large reflector in such a way that plane waves reflected by the same small reflector after having been reflected by said large reflector are so converted into spherical waves; said small reflector including means movable at least in part with respect to said large reflector for providing movement of said small reflector over a spherical surface centered at the center of curvature of said large reflector in such a way that this movement is a rotation around said center of curvature; wherein said small reflector is shaped for said plane waves to be converted into spherical waves centered at said center of curvature; said transducer being positioned on the convex side of said large reflector for emitting or receiving spherical waves centered at a fixed point; and fixed transmitting means being positioned in view of an opening through said large reflector for transmitting said waves between said small reflector and transducer through said opening in such a way that spherical waves centered at said center of curvature are converted into spherical waves centered at said fixed point.
 11. An emissive antenna as defined in claim 10, in which said transducer is directional and is mounted for adjustment with respect to the direction of emission and reception of waves about said fixed point, and wherein said movable means includes means for coordinately adjusting the relative positions of said transducer and said small reflector so that waves emitted by said transducer are reflected by said transmitting means at all times only over the entire useful surface of said small reflector.
 12. An emissive antenna as defined in claim 11, wherein said transmitting means between said transducer and said small reflector includes a third elliptical reflector connected to said large reflector on the convex side thereof to provide a surface contiguous thereto, and having the shape of a portion of an elongated ellipsoid a first focus thereof being located at the center of curvature of said large reflector and the second focus thereof being located at said fixed point. 